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Bisl 12. human body 01


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Britannica Illustrated Science Library 2009

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Bisl 12. human body 01

  1. 1. About the pagination of this eBook Due to the unique page numbering scheme of this book, the electronic pagination of the eBook does not match the pagination of the printed version. To navigate the text, please use the electronic Table of Contents that appears alongside the eBook or the Search function. For citation purposes, use the page numbers that appear in the text.
  2. 2. Encyclopædia Britannica, Inc. Chicago ■ London ■ New Delhi ■ Paris ■ Seoul ■ Sydney ■ Taipei ■ Tokyo Britannica Illustrated Science LibraryBritannica Illustrated Science Library HUMAN BODY IHUMAN BODY I
  3. 3. © 2008 Editorial Sol 90 All rights reserved. Idea and Concept of This Work: Editorial Sol 90 Project Management: Fabián Cassan Photo Credits: Corbis, ESA, Getty Images, Graphic News, NASA, National Geographic, Science Photo Library Illustrators: Guido Arroyo, Pablo Aschei, Carlos Francisco Bulzomi, Gustavo J. Caironi, Hernán Cañellas, Leonardo César, José Luis Corsetti, Vanina Farías, Manrique Fernández Buente, Joana Garrido, Celina Hilbert, Inkspot, Jorge Ivanovich, Iván Longuini, Isidro López, Diego Martín, Jorge Martínez, Marco Menco, Marcelo Morán, Ala de Mosca, Diego Mourelos, Laura Mourelos, Pablo Palastro, Eduardo Pérez, Javier Pérez, Ariel Piroyansky, Fernando Ramallo, Ariel Roldán, Marcel Socías, Néstor Taylor, Trebol Animation, Juan Venegas, Constanza Vicco, Coralia Vignau, Gustavo Yamin, 3DN, 3DOM studio Composition and Pre-press Services: Editorial Sol 90 Translation Services and Index: Publication Services, Inc. Portions © 2008 Encyclopædia Britannica, Inc. Encyclopædia Britannica, Britannica, and the thistle logo are registered trademarks of Encyclopædia Britannica, Inc. Britannica Illustrated Science Library Staff Editorial Michael Levy, Executive Editor, Core Editorial John Rafferty, Associate Editor, Earth Sciences William L. Hosch, Associate Editor, Mathematics and Computers Kara Rogers, Associate Editor, Life Sciences Rob Curley, Senior Editor, Science and Technology David Hayes, Special Projects Editor Art and Composition Steven N. Kapusta, Director Carol A. Gaines, Composition Supervisor Christine McCabe, Senior Illustrator Media Acquisition Kathy Nakamura, Manager Copy Department Sylvia Wallace, Director Julian Ronning, Supervisor Information Management and Retrieval Sheila Vasich, Information Architect Production Control Marilyn L. Barton Manufacturing Kim Gerber, Director Britannica Illustrated Science Library Britannica Illustrated Science Library Encyclopædia Britannica, Inc. Jacob E. Safra, Chairman of the Board Jorge Aguilar-Cauz, President Michael Ross, Senior Vice President, Corporate Development Dale H. Hoiberg, Senior Vice President and Editor Marsha Mackenzie, Director of Production International Standard Book Number (set): 978-1-59339-797-5 International Standard Book Number (volume): 978-1-59339-809-5 Britannica Illustrated Science Library: Human Body I 2008 Printed in China
  4. 4. Human Body I
  5. 5. Contents What Are We Made Of? Page 6 Bones and Muscles Page 18 Internal Systems and Organs Page 34 The Senses and Speech Page 68 Control Centers Page 80
  6. 6. What are cells like, and how do they form tissue? What is blood, and why are proteins so important? The heart, usually thought of as the wellspring of love and the emotions, is actually the engine of the circulatory system. It is because of the heart that all the cells of the body receive a constant supply of nutrients, oxygen, and other essential substances. The heart is so powerful that it pumps about 10 pints (4.7 l) of blood per minute. The nervous system is the most intricate of all the body's systems. It works A LIVING STRUCTURE The skeleton consists of 206 separate bones, which differ in form, size, and name. It supports and shapes the body, protects the internal organs, and—in the bone marrow of certain bones—manufactures various types of blood cells. every second of every day, gathering information about the organism and its surroundings and issuing instructions so that the organism can react. It is this computer that permits us to think and remember and that makes us who we are. T he nervous system is a complex network of sensory cells, originating in the brain and spinal cord, that transmits signals throughout the body, employing a caravan of chemical messengers to make sense of this marvelous complex that we catalogue as touch, taste, smell, hearing, and vision. In fact, at this precise moment, because of an extraordinary relationship between our eyes and our brain, we are able to see and understand what we are reading. Modern cameras are designed on the same basic principles as our eye, but they have never been able to equal the visual power of the eye. The focus and the automatic aperture of the human eye are perfect. Our ears share a similar complexity and allow us to have excellent hearing. The external ear operates by receiving sound waves in the air. Sound waves travel through the auditory canal and are transmitted by the bones of the intermediate ear toward the cochlea, which contains liquid and is spiraled like the shell of a small sea snail. The cochlea converts waves of air into vibrations of liquid, which are detected by special filaments in the ear that are of many lengths and that detect sound waves of different lengths. These filaments then transmit nerve impulses to the brain and provide us with our ability to interpret what we hear. This book will also tell you about the function of our skin, the largest organ of the body, which serves as an elastic barrier covering and protecting everything inside our bodies. Captivating images will show you how each of our extraordinary body systems function, and incredible facts will help you understand why the human body is so amazing. H ow can we understand what we are? What are we made of? Are we aware that all that we do—including reading this book—is the work of a marvelous machine? We know very little about how we are able to be conscious of our own actions; nevertheless, even though we are usually not very aware of it, this community of organs that is the body—an integrated system that includes the brain, heart, lungs, liver, kidneys, muscles, bones, skin, and endocrine glands— acts together in exquisitely regulated harmony. It is interesting that various mechanisms work together to keep the temperature of the body at 98.6° F (37° C); thanks to the dynamic structure of bones and cartilage, the body is maintained in perfect balance. The body also has a fantastic ability to transform the food it ingests into living tissues, bones, and teeth, all of which contribute to its growth. By this same process, we obtain the energy for working and playing. It is hard to imagine that not long ago the cells of the body of the person reading this book were autonomous and were duplicating themselves freely within the walls of a mother's uterus. Certainly no one reading this book could recognize herself or himself in those cells. Nevertheless, each cell carried within it the information necessary for the development of that person. Everything that happens inside us is truly fascinating. Therefore, we invite you to enjoy this book. It is full of incredible facts and illustrations that will show you the complex ways each part of the body works. A Perfect Machine
  7. 7. What Are We Made Of? T o understand the truest and most elementary characteristics of life, we must begin with the cell-the tiny organizing structure of life in all its forms. Most cells are too small to be observed with the naked eye, but they can be distinguished easily through an ordinary microscope. Human body tissues are groups of cells whose size and shape depend on the specific tissue to which they belong. Did you know that an embryo is a mass of rapidly dividing cells that continue to develop during infancy? We invite you to turn the page and discover many surprising things in this fascinating and complex world. UNDIVIDED ATTENTION 8-9 WATER AND LIQUIDS 10-11 THE CELL 12-13 MITOSIS 14-15 SYSTEMS OF THE BODY 16-17 MITOSIS An enlarged view that shows the process of mitosis, the most common form of cellular division
  8. 8. HUMAN BODY I 98 WHAT ARE WE MADE OF? Undivided Attention From birth the infant's brain cells develop rapidly, making connections that can shape all of life's experiences. The first three years are crucial. When neurons receive visual, auditory, or gustatory stimuli, they send messages that generate new physical connections with neighboring cells. The signals are sent through a gap called a synapse by means of a complex electrochemical process. What determines the formation of a person's synapses and neural networks? One key factor is believed to be the undivided attention and mental effort exerted by the person. THE SENSE OF TOUCH It is predominant in the fingers and hands. The information is transmitted through neurotransmitters, nerves that carry these impulses to the brain and that serve to detect sensations such as cold, heat, pressure, and pain. SKIN The skin is one of the most important organs of the body. It contains approximately five million tiny nerve endings that transmit sensations. LearningEach child has his or her own intellectual filter; the quality of the filter depends on undivided attention and on how the child responds to a broad variety of stimuli. BrainAt birth the infant brain contains 100 billion neurons. That is about as many nerve cells as there are stars in the entire Milky Way Galaxy! Then as the infant receives messages from the senses, the cerebral cortex begins its dynamic development. Respiration Respiration is usually an involuntary, automatic action that allows us to take in the oxygen we need from the air and exhale carbon dioxide. These gases are exchanged in the pulmonary alveoli. Neurons Each neuron in the brain can be connected with several thousand other neurons and is capable of receiving 100,000 signals per second. The signals travel through the nervous system at a speed of 225 miles per hour (360 km/h). Thanks to this complex communication network, the brain is capable of remembering, calculating, deciding, and thinking. A WORLD OF SENSATIONS The tongue recognizes four tastes (sweet, salty, sour, and bitter), and the nasal fossas contain cells that have more than 200 million filaments, called cilia, which are capable of detecting thousands of odors. DENDRITES They are the branches through which a neuron receives and sends messages. With this system each neuron can be stimulated by thousands of other neurons, which in turn can stimulate other neurons, and so forth. 3pounds (1.4 kg) IS THE WEIGHT OF A HUMAN BRAIN. 225 (360 km/h) THE VELOCITY OF THE NERVOUS SYSTEM'S SIGNALS miles per hour
  9. 9. HUMAN BODY I 1110 WHAT ARE WE MADE OF? Water and Fluids W ater is of such great importance that it makes up almost two thirds of the human body by weight. Water is present in all the tissues of the body. It plays a fundamental role in digestion and absorption and in the elimination of indigestible metabolic waste. Water also serves as the basis of the circulatory system, which uses blood to distribute nutrients to the entire body. Moreover, water helps maintain body temperature by expelling excess heat through the skin via perspiration and evaporation. Perspiration and evaporation of water account for most of the weight a person loses while exercising. N 3% NITROGEN Present in proteins and nucleic acids Water Balance and Food In its continuous process of taking in and eliminating water, one of the most important functions of the body is to maintain a continuous equilibrium between the water that enters and the water that leaves the body. Because the body does not have an organ or other place for storing water, quantities that are lost must be continuously replenished. The human body can survive for several weeks without taking in food, but going without water for the same length of time would have tragic consequences. The human being takes in about 2.5 to 3 quarts (2.5-3 l) of water per day. About half is taken in by drinking, and the rest comes from eating solid food. Some foods, such as fruits and vegetables, consist of 95 percent water. Eggs are 90 percent water, and red meat and fish are 60 to 70 percent water. HOW THIRST IS CONTROLLED Thirst is the sensation through which the nervous system informs its major organ, the brain, that the body needs water. The control center is the hypothalamus. If the concentration of plasma in the blood increases, it means the body is losing water. Dry mouth and a lack of saliva are also indications that the body needs water. HOW WATER IS ABSORBED Water for the body is obtained primarily by drinking and ingesting food and through internal chemical reactions. HOW WATER IS ELIMINATED Water is expelled not only with urine but also with sweat, through the elimination of feces, and through evaporation from the lungs and skin. 50% of the water comes from ingesting fluids. 35% of the water is obtained from food. 15% comes from metabolic activities. 60% is eliminated with urine. 18% is eliminated by sweating and through evaporation from the skin. 14% is eliminated during exhalation by the lungs. 8% is eliminated in excrement. C 18% CARBON Present in all organic molecules O 65% OXYGEN Present in water and in almost all organic molecules H 10% HYDROGEN Present in water, nutrients, and organic molecules Chemical Elements The body contains many chemical elements. The most common are oxygen, hydrogen, carbon, and nitrogen, which are found mainly in proteins. Nine chemical elements are present in moderate amounts, and the rest (such as zinc) are present only in very small amounts, so they are called trace elements. 0.004% IRON Fluids and tissues, bones, proteins. An iron deficiency causes anemia, whose symptoms include fatigue and paleness. Iron is essential for the formation of hemoglobin in the blood. THE PERCENTAGE OF A PERSON'S WEIGHT THAT IS DUE TO WATER. IN GENERAL, A 10 PERCENT LOSS OF WATER LEADS TO SERIOUS DISORDERS, AND A LOSS OF 20 PERCENT RESULTS IN DEATH. 60% SULFUR 0.3% Contained in numerous proteins, especially in the contractile proteins S POTASSIUM 0.3% Nerves and muscles; inside the cell K SODIUM 0.15% Fluids and tissues, in the form of salt Na MAGNESIUM 0.05% Lungs, kidneys, liver, thyroid, brain, muscles, heart Mg PHOSPHORUS 1% Urine, bonesP CHLORINE 0.2% maintains the equilibrium of water in the blood. Cl CALCIUM 1.5% Bones, lungs, kidneys, liver, thyroid, brain, muscles, heart Ca 0.0004% IODINE Urine, bones. When consumed, iodine passes into the blood and from there into the thyroid gland. Among its other functions, iodine is used by the thyroid to produce growth hormones for most of the organs and for brain development. Fe I Proteins Proteins are formed through the combination of the four most common chemical elements found in the body. Proteins include insulin, which is secreted by the pancreas to regulate the amount of sugar in the blood.
  10. 10. 12 WHAT ARE WE MADE OF? HUMAN BODY I 13 The Cell I t is the smallest unit of the human body—and of all living organisms—able to function autonomously. It is so small that it can be seen only with a microscope. Its essential parts are the nucleus and cytoplasm, which are surrounded by a membrane. Each cell reproduces independently through a process called mitosis. The animal kingdom does have single- celled organisms, but in a body such as that of a human being millions of cells are organized into tissues and organs. The word “cell” comes from Latin; it is the diminutive of cella, which means “hollow.” The science of studying cells is called cytology. MATHIAS SCHLEIDEN NUCLEUS ROUGH ENDOPLASMIC RETICULUM MITOCHONDRIA THEODOR SCHWANN Cell Theory Before the invention of the microscope, it was impossible to see cells. Some biological theories were therefore based on logical speculations rather than on observation. People believed in “spontaneous generation” because it was inconceivable that cells would regenerate. The development of the microscope, including that of an electronic version in the 20th century, made detailed observation of the internal structure of the cell possible. Robert Hooke was the first to see dead cells in 1665. In 1838 Mathias Schleiden observed living cells, and in 1839, in collaboration with Theodor Schwann, he developed the first theory of cells: that all living organisms consist of cells. Mitochondria The mitochondria provide large amounts of energy to the cell. They contain a variety of enzymes that, together with oxygen, degrade products derived from glycolysis and carry out cellular respiration. The amount of energy obtained in this process is almost 20 times as great as that released by glycolysis in the cytoplasm. Mitochondria are very different from other organelles because they have a unique structure: an external membrane enclosing an internal membrane with a great number of folds that delimit the internal area, or mitochondrial matrix. In addition, the mitochondria have a circular chromosome similar to that of bacteria that allows the mitochondria to replicate. Cells that need a relatively large amount of energy have many mitochondria because the cells reproduce frequently. TRANSPORT MECHANISMS The cell membrane is a semipermeable barrier. The cell exchanges nutrients and waste between its cytoplasm and the extracellular medium via passive and active transport mechanisms. DIFFUSION It is a passive transport mechanism in which the cell does not use energy. The particles that cross the cell membrane do so because of a concentration gradient. For example, water, oxygen, and carbon dioxide circulate by diffusion. FACILITATED DIFFUSION Passive transport in which substances, typically ions (electrically charged particles), that because of their size could not otherwise penetrate the cell's bilayer can do so through a pore consisting of proteins. Glucose enters the cell in this way. ACTIVE TRANSPORT It occurs by means of proteins and requires energy consumption by the cell because the direction of ion transport is against the concentration gradient. In some cells, such as neurons, the Na+/K+ pump uses active transport to move ions into or out of the cell. UNDER THE MICROSCOPE This cell has been magnified 4,000 times with an electron microscope. The nucleus is clearly visible, along with some typical organelles in the green- colored cytoplasm. CENTRIOLES They are cylindrical, hollow structures that are part of the cytoskeleton. NUCLEUS The nucleus consists of chromatin and regulates cell metabolism, growth, and reproduction. PORE A discontinuity in the nuclear membrane formed by proteins SMOOTH ENDOPLASMIC RETICULUM Various membranes, whose functions include transport and synthesis. They are tube-shaped and do not have ribosomes. VESICLE A closed compartment. It transports or digests cell products and residues. NUCLEOLE The nucleole can be single or multiple. The nucleole consists of ribonucleic acid and proteins. CELLULAR MEMBRANE The covering of the cell surrounding the cytoplasm. It is also known as the plasma membrane. VACUOLE Transports and stores ingested materials, waste, and water DNA It is organized into chromosomes within the nucleus. DNA is genetic material that contains information for the synthesis and replication of proteins. GOLGI APPARATUS This structure processes proteins produced by the rough endoplasmatic reticulum and places them in sacs called vesicles. CYTOPLASM The region located between the plasma membrane and the nucleus. It contains organelles. MITOCHONDRIA An organelle of the eukaryotic cell responsible for cellular respiration LYSOSOME This is the “stomach” of the cell because it breaks down waste molecules with its enzymes. RIBOSOME This organelle is where the last stages of protein synthesis take place. CYTOSKELETON Composed of fibers, the cytoskeleton is responsible for cell motion, or cytokinesis. ROUGH ENDOPLASMATIC RETICULUM A labyrinthine assembly of canals and membranous spaces that transport proteins and are involved in the synthesis of substances. PEROXISOME Organelles present in eukaryotes that function to metabolize and eliminate toxic substances from cells 100 billion THE AVERAGE NUMBER OF CELLS IN THE BODY OF AN ADULT. ONE CELL ALONE CAN DIVIDE UP TO 50 TIMES BEFORE DYING.
  11. 11. 14 WHAT ARE WE MADE OF? HUMAN BODY I 15 Mitosis I t is the cell-division process that results in the formation of cells that are genetically identical to the original (or mother) cell and to each other. The copies arise through replication and division of the chromosomes, or genetic material, in such a way that each of the daughter cells receives a similar inheritance of chromosomes. Mitosis is characteristic of eukaryotic cells. It ensures that the genetic information of the species and the individual is conserved. It also permits the multiplication of cells, which is necessary for the development, growth, and regeneration of the organism. The word “mitosis” comes from the Greek mitos, which means “thread,” or “weave.” THE ESTIMATED NUMBER OF CELLS REPLACED EVERY SECOND IN THE HUMAN BODY THROUGH CELLULAR DIVISION 50,000 50 MITOSES MARK THE LIFETIME OF A CELL AND ARE KNOWN AS THE “HAYFLICK LIMIT.” THIS IDEA IS NAMED AFTER LEONARD HAYFLICK, WHO IN 1961 DISCOVERED THAT THE SECTION OF DNA CALLED THE TELOMERE INFLUENCES CELL LIFE SPAN. Limit The Ever-Changing Skin Mitosis, or cellular division, occurs intensely within the skin, a fundamental organ of the sense of touch. The dead cells on the surface are continuously being replaced by new cells, which are produced by mitosis in the lowest, or basal, layer. From there the cells move upward until they reach the epidermis, the outer layer of the skin. A person typically sheds 30,000 dead skin cells every minute. Antioxidants Antioxidants are various types of substances (vitamins, enzymes, minerals, etc.) that combat the pernicious effects of free radicals—molecules that are highly reactive and form as a result of oxidation (when an atom loses an electron), which is often caused by coming into contact with oxygen. A consequence of this oxidative action is the aging of the body. One action of antioxidants is the regulation of mitosis. Preventive geriatrics has focused on using antioxidants to prevent disease and to slow aging, in part because properly regulated mitosis is fundamental to these processes. CENTROMERE SUPERFICIAL CELLS GRANULAR CELLS SPINOUS CELLS BASAL CELLS SPINDLE FILAMENT CELLULAR MEMBRANE CENTRIOLE CYTOPLASM CHROMATIN NUCLEUS NUCLEUS ORGANELLES SISTER CHROMOSOMES CHROMATID CHROMOSOME SHEDDING SUPERFICIAL CELLS LAYERS OF THE SKIN 1. INTERPHASE An independent stage that precedes mitosis. The chromatin consists of DNA. 2. PROPHASE In prophase the chromatin condenses to form chromosomes. The karyotheca (nuclear envelope) begins to disappear. Chromosomes are formed by two chromatids that are joined together by a centromere. 3. METAPHASE It is characterized by the appearance of the spindle. The centromere—the “center” of each chromosome—and the chromatids are joined together and align at the center of the spindle complex. The nuclear membrane disappears. 4. ANAPHASE In this crucial stage the copies of genetic information separate: the chromatids move apart and form sister chromosomes that migrate to opposite poles of the cell. 5. TELOPHASE The spindle disappears, and a new nuclear membrane begins to form around each new set of chromosomes. The membrane divides, resulting in two new cells that are identical daughters of the original cell. NUCLEUS
  12. 12. 16 WHAT ARE WE MADE OF? HUMAN BODY I 17 Systems of the Body T he body has various systems with different functions. These functions range from reproducing a cell to developing a new human being, from circulating the blood to capturing oxygen from the air, and from processing food through grinding and chemical transformations to absorbing nutrients and discarding waste. These functions act in harmony, and their interaction is surprisingly efficient. Muscular System Its function is to define the shape of the organism and protect it. The muscular system is essential for producing movement. It consists of muscles, organs made of fleshy tissue, and contractile cells. There are two types of muscles: striated and smooth. Striated muscles are attached to the bones and govern voluntary movement. Smooth muscles also obey the brain, but their movement is not under voluntary control. The myocardium, the muscle tissue of the heart, is unique and is in a class by itself. See page 30. Respiratory System Air from the external world enters the body through the upper airways. The central organs, the lungs, absorb oxygen and expel carbon dioxide. The lungs send oxygenated blood to all the cells via the circulatory system and in turn receive blood that requires purification. See page 46. Endocrine System The endocrine system is formed by glands that are distributed throughout the body. Its primary function is to produce approximately 50 hormones, the body's chemical messengers. The endocrine system secretes the hormones into the bloodstream so that they can reach the organs they are designed to influence, excite, or stimulate for such activities as growth and metabolism. See page 62. MALE The various male organs contribute one of the two cells needed to create a new human being. Two testicles (or gonads) and a penis are the principal organs of the system. The system is continuously active, producing millions of tiny cells called spermatozoa. See page 64. Reproductive System FEMALE A woman's internal organs are the vagina, the uterus, the ovaries, and the fallopian tubes. The basic functions of these organs are the production of ova and the facilitation of fertilization of an ovum by a spermatozoon (a mature male sperm cell). When fertilization occurs, it sets a group of processes in motion that result in pregnancy. See page 66. Skeletal System The skeleton, or skeletal system, is a solid structure consisting of bones that are supported by ligaments and cartilage. The main functions of the system are to give the body form and to support it, to cover and protect the internal organs, and to allow motion to occur. The skeleton also generates red blood cells (called erythrocytes). See page 20. Circulatory System This system carries blood to and from the heart and reaches the organs and cells in every part of the body. The supreme pump—the heart—drives the vital fluid—blood—through the arteries and collects it by means of the veins, with a continuous driving impulse that makes the heart the central engine of the body. See page 36. Nervous System The central nervous system consists of the brain, which is the principal organ of the body, along with the spinal cord. The peripheral nervous system consists of the cranial and spinal nerves. Together they send external and internal sensations to the brain, where the sensations are processed and responded to whether the person is asleep or awake. See page 82. Lymphatic System Its basic functions are twofold. One is to defend the body against foreign organisms, such as bacteria or viruses. The other is to transport interstitial fluid and substances from the digestive system into the bloodstream via the lymphatic drainage system. See page 42. Digestive System This system is a large tract that changes form and function as it goes from the mouth to the rectum and anus, passing through the pharynx, the esophagus, the stomach, and the small and large intestines. The liver and pancreas help process ingested food to extract its chemical components. Some of these components are welcome nutrients that are absorbed by the system, but others are useless substances that are discarded and eliminated. See page 50. Urinary System This system is a key system for homeostasis—that is, the equilibrium of the body's internal conditions. Its specific function is to regulate the amount of water and other substances in the body, discarding any that are toxic or that form an unnecessary surplus. The kidneys and the bladder are the urinary system's principal organs. The ureters transport the urine from the kidneys to the bladder, and the urethra carries the urine out of the body. See page 58.
  13. 13. JOINTS 28-29 MUSCULAR SYSTEM 30-31 MUSCLE FIBER 32-33 Bones and Muscles T he musculoskeletal system consists of the skeletal system of bones, attached to each other by ligaments to form joints, and the skeletal muscles, which use tendons to attach muscles to bone. The skeleton gives resistance and stability to the body and serves as a support structure for the muscles to work and produce movement. The bones also serve as a shield to protect the internal organs. In this chapter you will see in detail—even down to the inside of a muscle fiber—how each part works. Did you know that bones are constantly being regenerated and that, besides supporting the body, they are charged with producing red blood cells? In this chapter you will find incredible images, curiosities, and other information. SKELETON 20-21 BONE TISSUE 22-23 CRANIUM AND FACE 24-25 THE GREAT AXIS OF THE BODY 26-27 MUSCLES OF THE THORAX They play an important role in breathing by facilitating the contraction and expansion of the thoracic cavity.
  14. 14. Skeleton 20 BONES AND MUSCLES HUMAN BODY I 21 T he skeleton, or the skeletal system, is a strong, resistant structure made up of bones and their supporting ligaments and cartilage. The skeleton gives the body form and structure, covers and protects the internal organs, and makes movement possible. The bones store minerals and produce blood cells in the bone marrow. CRANIUM Holds and protects the brain INFERIOR MAXILLARY The only movable bone of the head, it forms the mandible (or jaw). SHOULDER BLADE Joins to the humerus Sexual Differences Bone structure is basically the same for both sexes. In women, though, the center opening of the pelvis is larger in order for an infant's head to pass through it during childbirth. The pelvic girdle is formed by two coxal, or hip, bones, which are joined in the rear with the sacral bone and are fused together in the front in the pubis. The pelvic girdle is involved in the joining of the hips, where it connects to the femur (thigh bone), serving the function of transmitting weight downward from the upper part of the body. The pelvic girdle and sacrum form the pelvis, which contains the organs of the digestive, reproductive, and urinary systems. Types of Bones Depending on their characteristics, such as size or shape, the bones of the human body are generally classified as follows: SHORT BONES: have a spherical or conical shape. The heel bone is a short bone. LONG BONES: have a central section that lies between two end points, or epiphyses. The femur is a long bone. FLAT BONES: form thin bony plates. Most bones of the cranium are flat bones. IRREGULAR BONES: take various shapes. The sphenoids (“wedgelike” bones) in the skull are irregular bones. SESAMOID BONES: are small and round. The patella and the bones between tendons and in the joints of the hands and feet are sesamoid bones. Well-Defined Form The structure of the skeleton can be described as a vertical column of chained vertebrae with a pair of limbs at each end and topped off by the cranium. The upper limbs, or arms, are connected to the shoulder blades and clavicles in what is called the scapular belt, and the lower limbs, or legs, are connected at the hips, or pelvic belt. The joints reach such a level of perfection that modern engineering often uses them as a model in the study of levers when designing such objects as cranes or desk lamps. Although the bones that make up the skeleton are solid, they have a flexible structure and to a large degree consist of spongy tissue. Nevertheless, a small bone is capable of supporting up to 9 tons without breaking. A comparable weight would crush a block of concrete. For a long time anatomists thought that bones themselves were not alive and that their strength merely provided support for the other organs. Modern medicine recognizes that bones are actively living, furnished with nerves and supplied with blood. The body has 80 of these bones, which belong to the part of the skeleton formed by the spinal column, the ribs, and the cranium. Axial Bones THESE COMPRISE THE OTHER 126 BONES: THOSE OF THE ARMS, SHOULDERS, HIPS, AND LEGS. THESE BONES PERMIT A GREAT RANGE OF MOTION. Appendicular Bones THE LENGTH OF THE SHORTEST BONE OF THE BODY. IT IS THE STIRRUP, A BONE IN THE EAR. 0.12 inches (3 mm) THE SIZE OF THE LARGEST BONE OF THE BODY, THE FEMUR 17inches (43 cm) In the Renaissance, the cradle of modernity, Leonardo da Vinci was one of the first to make precise drawings of human bones. Such drawings were needed for studying anatomy since there were no photographs or X-rays. Leonardo The total number of bones in the body is between 206 and 208, depending on the individual. The variation occurs with the supernumerary bones (bones of the skull) and the sesamoids (bones found in the joints of the hands and feet or embedded within tendons). 208 bones OCCIPITAL BONE Forms part of the back of the cranium CARPALS The bones of the wrist METACARPALS The bones of the palm of the hand COCCYX (TAILBONE) CLAVICLE Connects the shoulder blade with the sternum SPINAL COLUMN The core of the body's structure STERNUM Connected to the ribs by bands of cartilage PELVIS Contains and supports the abdominal organs HUMERUS The bone of the upper part of the arm, extending from the shoulder to the elbow SACRUM ILIUM Forms the posterior, or back, part of the pelvis RIBS Surround and protect the heart and the lungs CUBITUM The inside bone of the forearm RADIUS The shorter bone of the forearm CALCANUM Heel bone, the largest bone of the foot PHALANGES The bones of the fingers KNEECAP The knee bone, or patella, which is enveloped by tendons FIBULA The thin outside bone of the lower part of the leg FEMUR The thigh bone, the largest bone in the body. It extends from the hip to the knee. TIBIA The bone that supports most of the weight of the lower part of the leg TARSALS Ankle bones METATARSALS Five small bones between the ankle and the toes PHALANGES Bones of the toes SACRUM COXALS SACROILIAC The joint that transmits the weight of the body from the spinal column to the pelvis
  15. 15. TWO TYPES OF BONE CELLS 22 BONES AND MUSCLES HUMAN BODY I 23 Bony Tissue T he primary mission of the bones is to protect the organs of the body. Bones are solid and resilient, which allows them to endure blows and prevent damage to the internal organs. The hard exterior is balanced by the internal spongy part. Over a person's lifetime bones are continuously regenerated; this process continues even after a person reaches maturity. Besides supporting the body and enabling movement, the bones are charged with producing red globules: thousands of millions of new cells are produced daily in the bone marrow, in a never-ending process of replacing old cells. BLOOD VESSELS carry blood to and from the bones to the rest of the body. PERIOSTEUM A thin membrane that covers the exterior surface of the bone OSTEOBLAST produces osseous, or bone, tissue, which maintains the strength of the bone. Bone Marrow A soft, fatty substance that fills the central cavities and produces red blood cells. Over time bone marrow in the large bones loses its ability to produce red blood cells. OSTEOCLAST breaks down the tissue so that it can be replaced with newer tissue. IN AN INFANT In a newborn infant the ends of the long bone (epiphyses) are made of cartilage. Between the bone shaft and an epiphysis, an area called a “growth plate” produces cartilage to lengthen the bone. EPIPHYSIS Secondary ossification centers, to aid in long-term bone growth and to shape the bones GROWTH PLATE Continues to act, depositing bone on the diaphysis face of the growth plate GROWTH PLATE consists of cartilage. It deposits new bone on the diaphysis face of the growth plate so the bone will grow. EPIPHYSIS The end of a long bone, which at birth consists of cartilage Canals The structure of compact bone, showing concentric rings, or laminae, and canals called Havers conduits. COMPACT BONE Exterior covering, dense and heavy. It is one of the hardest materials in the body. FUSION Epiphysis, growth plates, and diaphysis are transformed into continuous bone. DIAPHYSIS Water is deposited in the new bone. DIAPHYSIS Also called “bone shaft” Calcium and Marrow All the hard parts that form the skeleton in vertebrates, such as the human being, are called bones. They may be hard, but they are nevertheless formed by a structure of living cells, nerves, and blood vessels, and they are capable of withstanding pressure of up to 1,000 pounds (450 kg). Because of their constitution and characteristics, they can mend themselves when fractured. A resistant exterior layer called the periosteum covers the outside of the compact bone. The endosteum, a thin layer of connective tissue lining the interior cavity of bone, contains the trabecular, or spongy mass, which is characterized by innumerable pores. The bone marrow, located in the center of the large bones, acts as a virtual red blood-cell factory and is also known as the medulla ossea. Minerals such as calcium go into making the bones. The fact that calcium is found in foods such as milk explains why healthy bones are usually associated with drinking a lot of milk. Calcium and phosphorous, among other chemical substances, give bones strength and rigidity. Proteins such as collagen provide flexibility and elasticity. Evolution of Bone Bone development is completed at about 18 or 20 years of age in a process that begins with an infant's bones, which are largely cartilage, and continues with the ongoing generation of bone in the person as an adult. Calcium is an indispensable element for the healthy development of bones through this process. Until the age of six months, an intake of 0.007 ounce (210 mg) of calcium per day is recommended. Spongy Bone Internal layer of the bone. It is a network in the form of a honeycomb consisting of struts or rigid partitions called trabeculae, with spaces or cavities between them. The osseous tissue consists of two types of cells, osteoblasts and osteoclasts. Both are produced by the bone marrow, and their interaction and equilibrium ensure the integrity and continuous renewal of the bone. An osteoclast reabsorbs bone tissue, leaving empty spaces, and an osteoblast fills them. The function of the osteocytes, a variant of the osteoblasts, is to maintain the shape of the bone. WHY FRACTURES HEAL Bone has great regenerative capacity. Bone tissue has an extraordinary ability to repair itself after a fracture through processes that include the relatively rapid generation of cells. Medicine can guide these processes to cure other lesions, deformities, etc. A A fracture occurs, and the blood cells coagulate to seal the broken blood vessels. 1 IN A CHILD In a child ossification continues to completion during epiphysis, generating long-term bone growth. 2 IN AN ADULT The process is complete when a person reaches about 18 years of age. The epiphysis, growth plates, and bone shaft fuse and become ossified into a continuous bone. 3 B Over a few days a fibrous mesh forms, which closes the ends of the bone and replaces the coagulate. C Within one to two weeks new spongy bone develops on a base of fibrous tissue. The spaces created by the fracture are filled, and, finally, the ends are fused. D Within two to three months, new blood vessels have developed. Compact bone forms on the bony callous. VEIN ARTERY DIAPHYSIS contains the bone marrow, which produces red blood cells and has a network of blood vessels.
  16. 16. 24 BONES AND MUSCLES HUMAN BODY I 25 Cranium and Face T he cranium surrounds and protects the brain, cerebellum, and cerebral trunk (sometimes called the encephalus). In an adult the cranium consists of eight bones that form the skull and the base of the cranium. The face is the anterior part of the skull. It consists of 14 bones, all of which are fixed except the lower maxillary, which makes up the mandible. The total number of bones in the head as a whole exceeds the total of the face and cranium (22) because it includes the little bones of the middle ear. Cranial Sinuses The sinuses are air-filled cavities whose principal known function is to humidify and heat the air that enters the respiratory tract via the nose. The sinuses reduce the weight of the head, and they also act as resonance cavities, giving the voice its timbre. The sinuses are covered by a moist membrane and are connected via small openings with the interior of the nasal cavity. When the sinuses become inflamed or filled with mucus, there is a risk of infection. Vibration When a person speaks, the bones of the cranium vibrate. In Japan a technology was developed based on this vibration. In 2006 the firefighters of the Madrid municipality in Spain adopted this technology. A helmet, furnished with a cranial contact microphone, amplifies the vibrations produced in the bones of the cranium during speech and sends them to radio equipment. FRONTAL SINUS ETHMOID SINUS SPHENOID SINUS MAXILLARY SINUS Foramen Magnum In Latin this term means “big hole.” It is a circular opening, also called the occipital orifice, which is located at the base of the cranium. The foramen magnum allows for the passage of the spinal column, the medulla oblongata, the vertebral arteries, and the spinal nerve. The placement of the foramen magnum toward the bottom of the skull is associated with more highly evolved species. The cranium can be compared to a sphere, which consists of separate bones at birth and closes completely at maturity. The narrow separations between the bones, which appear as lines in the fetus for the first months of its life, are called sutures. Spaces called fontanels form where the sutures meet. Their separation has the functional purpose of allowing the brain to grow. Therefore, when brain growth is complete, the sphere closes tightly, because its function is to protect the brain. Cranial Bones (8) PARIETAL (2) The superior and lateral parts of the cranium OCCIPITAL (1) Together with the temporals, it forms the base of the cranium. FRONTAL (1) It makes up the forehead. TEMPORAL (2) The lateral part of the cranium SPHENOID (1) The front part of the base of the cranium and part of the orbital bone (eye socket) ETHMOID (1) Upper part of the nasal cavity Facial Bones (14) ZYGOMATIC (2) The cheekbones PALATINES (2) Internal bones that form the roof of the mouth LACHRYMAL BONES (2) form the eye socket. SUPERIOR MAXILLARIES (2) The upper mandible NASAL CONCHAS (2) Independent of the ethmoid conchas VOMER (1) divides the nasal cavity into two halves. NASAL BONE (2) forms the bridge of the nose (the rest of the nose is cartilage). INFERIOR MAXILLARY (1) constitutes the mandible and is the only facial bone that can move freely. FORAMEN MAGNUM 22THE TOTAL NUMBER OF BONES IN THE CRANIUM 83(1,360 cu cm) THE TYPICAL VOLUME OF THE CRANIUM Sutures and Fontanels cubic inches 9THE WEIGHT OF AN ADULT HUMAN HEAD pounds (4 kg)
  17. 17. 26 BONES AND MUSCLES HUMAN BODY I 27 T he vertebral, or spinal, column is the flexible axis that lends support to the body. It consists of a series of bones jointed together in a line, or chain, called the vertebrae. The spinal column forms a protective inner channel through which the spinal cord runs. The ribs perform a similar function, wrapping and shielding the vital internal organs, which include the heart and lungs. Downwards All the vertebrae except the cervical axis and atlas have a cylindrical body, which gives them a particular characteristic: as they approach the pelvis they tend to be longer and stronger. CARPALS (8) 1. LUNATE 2. PISIFORM 3. TRIQUETRUM 4. TRAPEZIUM 5. TRAPEZOID 6. CAPITATE 7. SCAPHOID 8. HAMATE TARSUS (7) 1. MEDIAL CUNEIFORM 2. INTERMEDIATE CUNEIFORM 3. LATERAL CUNEIFORM 4. TALUS 5. TARSAL SCAPHOIDS 6. CALCANEUS 7. CUBOIDS METACARPALS (5) CARPALS (8) METATARSALS (5) PHALANGES (14) PHALANGES (14) Bones of the Hands and Feet Each hand (see the drawing below) has 27 bones, and each foot (see above) has 26. The hand has great mobility, and each of its fingers (five in all) has three phalanges (distal, medial, and proximal), except for the thumb, which has two. The complex of carpal bones makes up the wrist and is connected to the forearm. The metacarpal bone sustains the medial part. The feet function in a similar manner; the toes have first, second, and third phalanges, except for the big toe. Stability and Motion The vertebrae have a centrum that allows them to support the body's weight, each vertebra upon the next, as well as the weight of the rest of the body. The vertebrae also have extensions that allow them to articulate with other vertebrae or act as supports for the ligaments and the muscles. This system gives the axis of the body both strength and flexibility. In addition, most of the nerves of the peripheral system (that is, those responsible for voluntary movement, for pain, and for the sense of touch) are connected to the spinal cord inside the spinal column. In the centrum the vertebrae are separated from each other by intervertebral disks that are made of cartilage and have a gelatinous interior. When an intervertebral disk is damaged, some of this material can escape and pinch a nerve. This condition, called a herniated disk, can be very painful. 1 1 2 3 4 7 8 5 6 2 3 7 6 4 5 SACRUM This bone is formed by five fused vertebrae. COCCYX This bone is composed of four fused vertebrae. The Ribs and the Rib Cage The 12 pairs of ribs, which also extend from the spinal column, protect the heart, lungs, major arteries, and liver. These bones are flat and curved. The seven upper pairs are called “true ribs,” and they are connected to the sternum (a flat bone consisting of fused segments) by cartilage. The next two or three pairs (called “false ribs”) are connected indirectly. The remaining pairs (“floating ribs”) are not attached to the sternum. The rib cage, formed by the ribs and its muscles, is flexible: it expands and contracts during breathing. SACRAL CANAL Nerves pass through the sacral canal. BLADE LUMBAR VERTEBRAE There are five of them, and they bear the weight of the upper part of the body. The Three Curves The three types of natural curvature in the spinal column include cervical lordosis (forward, or inward, bending in the cervical region of the spine), kyphosis (outward bending of the thoracic region of the spine), and lumbar lordosis (forward bending of the lower back). Shown here is the right side of the spinal column. AXIS The second cervical vertebra. Together with the atlas, it permits the movement of the head. CERVICAL These seven vertebrae (including the atlas and the axis) support the head and the neck. THORACIC, OR DORSAL, VERTEBRAE There are 12, and they are joined to the ribs. ATLAS This bone is the first of the seven cervical bones; it unites the spinal column with the head. PARTS OF THE VERTEBRAE 1. SPINAL APOPHYSIS 2. TRANSVERSE APOPHYSIS (2) 3. ARTICULAR APOPHYSIS (4) (2 SUPERIOR AND 2 INFERIOR) 4. LAMINAE (2) 5. PEDICULAE (2) 6. FORAMEN MAGNUM 7. BODY 1 2 3 7 6 4 5 STERNUM LUNG LIVER DIAPHRAGM HEART SPLEEN STOMACH RIB CARTILAGE 33 bones OR VERTEBRAE, MAKE UP THE SPINAL COLUMN. DEPENDING ON THE INDIVIDUAL, SOMETIMES THERE ARE 34. THEY ARE CONNECTED BY DISKS OF CARTILAGE THAT ACT AS SHOCK ABSORBERS. THE SACRUM AND THE COCCYX ARE A RUDIMENTARY TAIL LOST DURING EVOLUTION. The Great Axis of the Body
  18. 18. HUMAN BODY I 2928 BONES AND MUSCLES The Knee The knee is the biggest joint of the body. It maintains its stability because it is constrained by four ligaments: the anterior and posterior cruciate and the internal and external lateral. The ligaments link the femur (the thigh bone) with the tibia (a bone of the leg). The knee is protected by the kneecap, a bony disk covered with cartilage that encases the anterior and superior part of the knee joint. Like the majority of the joints, it is synovial. FEMUR The thigh bone, which is the upper region of the lower limb MUSCLE MUSCLE TIBIA The larger of the two bones of the lower leg KNEECAP Protective bony disk covered with cartilage SYNOVIAL MEMBRANE produces the synovial liquid. PATELLAR LIGAMENT This ligament crosses over the kneecap and encases it. MENISCUS Fibrous cartilage that helps the weight- supporting bones to absorb a blow EXTERNAL LIGAMENTS Stabilize the joint during movement. The knee also has internal ligaments. ARTERY The femoral artery (artery of the femur) changes into the popliteal artery at the posterior face of the knee. Like all arteries it carries oxygenated blood from the heart. Joints T hey are the structures where two or more bones come together, either directly or by means of strong fibrous cords called ligaments. The skeleton has movement thanks to its joints. Most joints, like the knee, are synovial joints. They are characterized by mobility, versatility, and lubrication. The muscles that surround them contract to cause movement. When they work as a whole, the bones, muscles, and joints—together with the tendons, ligaments, and cartilage—constitute a grand system that governs the motor activity of the body and allows us to carry out our daily physical activities. Flexion Extension Circumduction MOVEMENTS The complex of joints, together with the muscles and bones, allows the body to perform numerous actions, with movements that include turns and twists. Hypermobility The versatility of the joints refers to their characteristic range of motion. Just as there are mobile, semimobile, and fixed joints, there is also a group of joints that are hypermobile. Such joints are less common but are easily recognizable, especially in children and adults who have not lost the flexibility of their joints. The elbows, wrists, fingers, and knees can at an early age and in certain individuals have a greater-than-normal range of motion. For people with hypermobile joints this extra range of motion can be accomplished without difficulty or risk of dislocation. Rotation Abduction Dorsiflexion Plantar Flexion Adduction FIBULA The smallest bone of the lower leg A CHARACTERISTIC OF THE JOINTS IS THAT THEY CAN MAKE A SOUND, SUCH AS THAT MADE WHEN SOMEONE CRACKS HER OR HIS KNUCKLES. THIS IS BECAUSE THERE IS AN EXPLOSIVE RELEASE OF GAS THAT PERMITS A SHOCK-ABSORBING FLUID TO FLOW IN THE JOINT. Noise IN THIS YEAR PROFESSOR KENJI TAKAGI OF JAPAN USED A CYSTOSCOPE FOR THE FIRST INTERNAL OBSERVATION OF THE KNEE. Technological advances now permit arthroscopy to make precise observations for diagnosis. 1918 IN THE FORM OF A PIVOT The joint of the upper bones of the neck. One bone is nested within the other and turns within it. This is the case of the atlas and the axis, in the upper part of the neck, which allow the head to turn from side to side. This is a limited movement. SPHEROID Articulation of the shoulder. A bone that has a spherical end that can be inserted into another bone. The motion is extremely varied, such as that of the shoulders. HINGE Articulation of the knee. One bone with a cylindrical end is inserted into the patellar groove of the other. There is flexion and extension, as in the knee. PLANE Articulation of the foot. Two surfaces that slide, one on top of the other, forward, backward, and sideways, as in some joints of the foot and wrist. ELLIPSOID The joint between the humerus and the radius. A bone with an oval end is inserted into the cavity of another bone. The motion is varied, but there is minimal rotation, as is the case for the wrists. BASAL JOINT The joint at the base of the thumb. The ends of the two bones come together at a right angle. This allows them to turn, and they move backward and forward, as occurs with the thumbs. Mobile These are also called diarthroses; they are the joints with the greatest range of motion. The ends of the bones linked together are structured in various ways that facilitate their movement relative to each other, while ensuring the stability of the joint. Most joints in the body are of this type. Semimobile Also known as amphiarthroses. The surfaces of the bone that make contact have cartilaginous tissue. One example is the vertebral joints: they have little individual movement, but as a whole they have ample flexion, extension, and rotation. Fixed Also known as synarthroses. Most fixed joints are found in the cranium and have no need for motion because their primary function is to protect internal organs. They are connected by bone growth or fibrous cartilage and are extremely rigid and very tough. Where the patellar tendon connects to the bone
  19. 19. Muscular System 30 BONES AND MUSCLES HUMAN BODY I 31 T he muscles are organs formed by fleshy tissue consisting of contractile cells. They are divided into striated, smooth, and, in a unique case, cardiac (the myocardium is the muscular tissue of the heart). Muscles shape and protect the organism. The muscles of the skeleton are attached to the bones to permit voluntary movement, which is consciously directed by the brain. The smooth muscles are also directed by the brain, but their motion is not voluntary, as in the case of digestion. These muscles get most of their energy from alimentary carbohydrates, which can be stored in the liver and muscles in the form of glycogen and can later pass into the blood and be used as glucose. When a person makes a physical effort, there is an increased demand for both oxygen and glucose, as well as an increase in blood circulation. A lack of glucose leads to fatigue. FRONTAL MUSCLE wrinkles the forehead. ORBICULAR MUSCLE allows blinking. STERNOCLEIDOMASTOID allows the head to turn and move forward. PECTORALIS MAJOR stretches the arm forward. It turns it and brings it close to the body. BRACHIAL BICEP bends the arm at the elbow. EXTERNAL OBLIQUE turns the trunk and bends it to both sides. RECTUS ABDOMINIS bends the trunk forward. SPLENIUS keeps the head erect. TRAPEZIUM turns the head and the shoulders forward. It stabilizes the shoulders. OCCIPITAL pulls the scalp backward. ANTERIOR TIBIA lifts the foot and is connected to the metatarsal bones of the foot. EXTENSOR DIGITORUM LONGUS Called the “pedis,” it connects to the dorsal part of the foot. FEMORAL QUADRICEPS A powerful muscular complex that stretches the knee when a person runs and kicks. The quadriceps include four muscles, with their upper extremes connected to the femur and the pelvis and their lower extremes anchored in the tibia. When the muscles contract, the lower part of the leg is thrust forward. STRIATED They are also called “skeletal” (because they cover the skeleton) and “voluntary.” They are composed of cells and fibers that contract rapidly. CARDIAC Composed of small interconnected fibers, which maintain the rhythmic and continuous pumping of the heart. SMOOTH Perform unconscious actions such as digestion. Their fibers contract slowly over an extended period of time. ACHILLES TENDON connects the gastrocnemius to the calcaneus bone (talus bone). GASTROCNEMIUS Also called “twins.” There are two, and they extend from the femur to the calcaneus. They bend the leg. DELTOID A triangular muscle surrounding the shoulder. It lifts the arm to the side and causes it to swing when walking. FEMORAL BICEP bends the leg at the knee. Clearly, a lot fewer muscles are needed to smile than to frown. FOREHEAD WRINKLE THE EYEBROWS UPPER LIP ELEVATOR ZYGOMATIC MINOR MUSCLES FOR FROWNING MUSCLES FOR SMILING GLUTEUS MAXIMUS extends from the hip to the thigh. BRACHIAL TRICEP stretches the arm at the elbow. When the Skeleton Moves The great number of muscles of voluntary action available to the human body makes possible thousands of distinct movements. Actions from the simple blink of an eyelid to the twisting of a belt are accomplished by muscular action. The eye muscles involve the most activity because they carry out 100,000 movements per day. Some 30 muscles control all the movements of the face and define an infinite possible combination of facial expressions. It is calculated that to pronounce one word, the organs for speech and respiration move some 70 muscles. The stirrup muscle, which controls the stirrup of the ear, is one of the smallest in the body. It measures approximately 0.05 inch (1.2 mm). There are other muscles that are very large, including the latissimus dorsi of the shoulder. The foot has 40 muscles and more than 200 ligaments. Because the muscles are connected by a great number of nerves, a lesion or blow causes the brain to react, producing pain. Approximately 40 percent of the total weight of the body consists of the muscular system. When the organism reduces the quantity of calories it normally ingests (for example, when a person goes on a diet), the first thing the body loses is water, which is reflected in a rapid weight loss. Then the metabolism adapts to the diet, and the body resorts to using up muscle tissue before drawing on the fats stored for burning calories. For this reason, when the diet begins this second phase, the consequences can be lack of vigor and loss of muscle tone, which is recovered when the diet returns to normal. OR VOLUNTARY MUSCLES ARE IN THE TYPICAL HUMAN BODY. 650 skeletal muscles RISORIUS ZYGOMATIC MAJOR OCULAR ORBIT NASAL LOWER LIP DEPRESSOR MENTALIS MUSCLE PLATYSMA THE THREE TYPES OF MUSCLES
  20. 20. HUMAN BODY I 3332 BONES AND MUSCLES Muscular Fiber A fiber is the long, thin cell that, when organized by the hundreds into groups called fascicles, constitutes the muscles. It is shaped like an elongated cylinder. The amount of fiber present varies according to the function accomplished by each muscle. Fibers are classified as white, which contract readily for actions that require force and power, and red, which perform slow contractions in movements of force and sustained traction. Each muscle fiber contains in its structure numerous filaments called myofibers. Myofibers, in turn, have two classes of protein filaments: myosin, also called thick filaments, and actin, or thin filaments. Both kinds of fibers are arranged in tiny matrices called sarcomeres. MUSCLE Composed of hundreds of fiber bundles MUSCLE FIBER MYOFIBRIL A filament that usually has a sticklike form and that is found inside a muscle fiber PERINEURIUM The sheath of connective tissue that surrounds each fascicle AXON The extension of the nerve cell, whose end makes contact with the muscle and other cells SARCOMERE Each small internal cylinder of the myofibril, consisting of actin and myosin CONNECTED FILAMENTS Actin and myosin are linked through these filaments. MYOSIN AND ACTIN FILAMENTS The actin and myosin filaments overlap each other to cause muscular contraction. Z BAND marks the boundary between sarcomeres. THE HEAD OF A MOLECULE The head of a myosin molecule extends. It makes contact with the actin, and the myocin and actin overlap each other, producing a muscular contraction. THICK MYOFILAMENT (MYOSIN) The principal protein in the thick muscles, which enables the reaction that leads to contraction THIN MYOFILAMENT (ACTIN) determines muscular contraction when linked with myosin. The order to contract given by the nervous system ceases, and the muscle fibers return to a position of rest. This happens to all muscles, regardless of the duration of contraction. Relaxation The nervous system orders the muscle fibers, no matter which type, to shorten. In order to create muscle contraction, calcium is released within the muscle cell, which allows the actin and the myosin to come together and overlap each other. Contraction THE LENGTH A MUSCLE FIBER CAN REACH 12 inches (30 cm) THE POTENTIAL CONTRACTION OF A MUSCLE FIBER IN TERMS OF THE FIBER'S LENGTH 70% Marathon runners may have as much as 90 percent red, or slow, fibers in their twin muscles. Champions in the 100-meter dash have only 20 to 25 percent. Running Specialization The quantity of muscle fiber varies according to the size and function of the muscle. Also, the same muscle can combine white fibers (rapid contracters) and red fibers (slow contracters). Even though their percentages differ from one person to the next, the composition of the muscles of the upper limbs tends to be the same as that of the lower in the same person. In other words, the relation between motor neurons and muscle fibers is inscribed in a person's genes. Depending on the type of neuron that stimulates them, the fibers are differentiated into slow fibers (when the neuron or motor neuron innervates between five and 180 fibers) and rapid fibers (when the neuron innervates between 200 and 800 fibers). The neurons and the fiber constitute what is called a motor unit. A Bone Lever In a lever system a force is applied to one end of a bar that is placed on a fixed point of support (the fulcrum) to move a weight at the other end. In the body the bones are the bars, and the joints act like a fulcrum. The force is proportional to the muscular contraction. FASCICLE Each of the hundreds of fiber bundles that make up one muscle CAPILLARIES These bring blood to the muscle fibers. FIRST CLASS LEVER The joint is located between the muscular contraction and the body part that is moved. Examples are the muscles that pull the cranium to move the head backward. 1 SECOND CLASS LEVER The body part that is moved is located between the joint and the muscular contraction. Examples are the muscles of the calf that lift the heel. 2 THIRD CLASS LEVER The most common type in the body, where the muscular contraction is applied between the joint and the body part moved. Examples are the muscles that bend the elbow. 3 Opposites The muscles contract or relax according to the movement to be accomplished. To make the brain's directive take effect, the muscles involved carry out opposing actions. EXTENDED ARM FLEXED ARM Relaxed Biceps Contracted Triceps Contracted Biceps Relaxed Triceps Force Fulcrum Weight Force Fulcrum Weight Force Fulcrum Weight
  21. 21. KIDNEYS 60-61 ENDOCRINE SYSTEM 62-63 MALE REPRODUCTIVE SYSTEM 64-65 FEMALE REPRODUCTIVE SYSTEM 66-67 Internal Systems and Organs I t is difficult to explain that the sexual attraction between a man and woman—something that appears to be so natural and intimate—is a chemical phenomenon. What is certain is that when a couple feels they are in love, it is because hormones have gone into action. Without them, amorous thoughts and sexual fantasies would be drab and dull. We invite you to find out to what extent hormones determine many of our actions and also to investigate in detail, one by one, how the body's systems function. You will learn to understand how various organs of the body work as a team. Although each organ accomplishes specific tasks on its own, they all communicate with each other, and together they form a complete human being. LUNGS 48-49 DIGESTIVE SYSTEM 50-51 STOMACH 52-53 LIVER, PANCREAS, BILE 54-55 LARGE AND SMALL INTESTINE 56-57 URINARY SYSTEM 58-59 CIRCULATORY SYSTEM 36-37 ALL ABOUT THE HEART 38-39 COMPONENTS OF THE BLOOD 40-41 LYMPHATIC SYSTEM 42-43 GANGLIA 44-45 RESPIRATORY SYSTEM 46-47 THE CHEMISTRY OF LOVE Even a light kiss results in the release of adrenaline, causing a sensation of euphoria and joy.
  22. 22. Circulatory System 36 INTERNAL SYSTEMS AND ORGANS HUMAN BODY I 37 I ts function is to carry blood to and from all the organs of the body. To drive the constant movement of the blood, the system uses the pumping of the heart, the organ that acts as the system's engine. The arteries bring oxygen-rich blood to all the cells, and the veins retrieve the blood so that it can be oxygenated once again and so that wastes can be removed. Veins The veins are the conduits that transport deoxygenated blood back toward the heart after it has traveled to different parts of the body. The veins have thin walls with less muscular fiber and less elasticity than the arteries. The principal veins have valves to prevent the reflux of blood, forcing it to travel in only one direction. Capillaries These are branchings of the arterioles, small vessels into which the arteries are subdivided. The capillaries are tiny, and they come together to form small veins, which combine to form larger veins. The capillaries are crucial in the exchange of oxygen, nutrients, and waste, and they form a network to carry out this activity. Ten capillaries together are as thick as a human hair. THE EXTERNAL DIAMETER OF THE AORTA (THE LARGEST ARTERY) AND THE VENA CAVA (THE LARGEST VEIN) 1inch (2.5 cm) TEMPORAL ARTERY runs along the side of the head. SUPERIOR VENA CAVA brings the blood from the upper part of the body for purification. The superior vena cava and the inferior vena cava together form the largest vein. INFERIOR VENA CAVA takes blood arriving from the area below the diaphragm and brings it up to the heart. LEFT PRIMITIVE ILIAC VEIN This is the primary vein of the hip area. JUGULAR VEINS There are two on each side of the neck: the internal and the external. LEFT CAROTID ARTERY runs along the neck and supplies blood to the head. AORTIC ARTERY (AORTA) The body's principal artery HEART The great engine HUMERAL ARTERY (Axillary) The right one arises from the brachiocephalic trunk and the left from the aortic arch. TUNICA ADVENTITIA ELASTIC MEMBRANET TUNICA MEDIA OUTSIDE OF TUNICA INTIMA INSIDE OF TUNICA INTIMA PULMONARY ARTERY carries blood to the lungs. PALMAR VENOUS ARCH channels the hand's venal blood flow. FEMORAL ARTERY carries oxygenated blood along the thigh. TIBIAL ARTERY irrigates the leg. BLOOD DISTRIBUTION DURING CIRCULATION SUBCLAVIAN VEIN connects the axillary with the superior vena cava. A System That Goes Around The center of the system is the heart, which, together with a network of vessels, forms the cardiovascular machinery. This vital engine beats more than 30 million times a year-approximately 2 billion times in a person's lifetime. With each beat it pumps about 5 cubic inches (82 ml) of blood. This means that an adult heart could fill a 2,000-gallon (8,000-l) tank in just one day. Beginning at the heart, the circulatory system completes two circuits: the main, or systemic, circulation via the aortic artery and the minor, or pulmonary, circulation. The main circulation brings oxygenated blood to the capillary system, where the veins are formed; the minor circulation brings oxygen-poor blood through the pulmonary artery to be enriched with oxygen and to have carbon dioxide removed from it, a process called hematosis. Other secondary circuits are the hepatic portal system and the hypophyseal portal system. TRUNCUS OF THE PORTAL VEIN It terminates in the sinusoids of the liver. RENAL VEIN Blood exits the kidneys through this vein. TEMPORAL VEIN runs along the side of the head. RADIAL ARTERY runs along the radial side of the forearm. FEMORAL VEIN runs along the thigh, channeling the deoxygenated blood toward the heart. TIBIAL VEIN LEFT PRIMITIVE ILIAC ARTERY provides blood to the pelvis and the legs. THE TOTAL LENGTH OF THE BLOOD VESSELS. NINETY- EIGHT PERCENT OF THEM ARE CAPILLARIES. 60,000miles (100,000 km) THE RANGE IN DIAMETER OF CAPILLARIES THE AVERAGE LENGTH IS 0.04 INCH (1 MM). 0.00001 to 0.1 inch (0.001 to 0.2 mm) 67% VEINS 17% ARTERIES 11% HEART 5% CAPILLARIES EXTERNAL MEMBRANE INTERNAL COVERING VALVE MUSCULAR MEMBRANE CAPILLARY WALL NUCLEUS Arteries Muscular elastic blood vessels. Their function is to bring oxygenated blood from the heart (from the primary artery, the aorta) to all the cells of the body. Arteries have thick walls, allowing them to withstand the high pressure of the blood.
  23. 23. 38 INTERNAL SYSTEMS AND ORGANS HUMAN BODY I 39 T he heart is the engine of the circulatory apparatus: it supplies 10 pints (4.7 l) of blood per minute. Its rhythmic pumping ensures that blood arrives in every part of the body. The heart beats between 60 and 100 times per minute in a person at rest and up to 200 times per minute during activity. The heart is a hollow organ, the size of a fist; it is enclosed in the thoracic cavity in the center of the chest above the diaphragm. The name of the stomach's entrance, or cardias, comes from the Greek word for heart, kardia. Histologically, one can distinguish three layers of tissue in the heart, starting from the inside out: the endocardium, the myocardium, and the pericardium. DIASTOLIC The atria and the ventricles are relaxed. The blood, supercharged with carbon dioxide, flows from all the corners of the body and enters the right atrium, while the blood that was oxygenated through the work of the lungs returns to the left part of the heart. THE SEQUENCE OF THE HEARTBEAT SUPERIOR VENA CAVA brings the blood to be oxygenated from the lower part of the body. RIGHT ATRIUM It sends the blood through the tricuspid valve to the right ventricle. LEFT VENTRICLE receives the oxygenated blood via the mitral valve. LEFT ATRIUM receives the oxygenated blood from the lungs TRICUSPID VALVE opens so that blood can pass from the atrium to the ventricle and then closes to prevent it from going back. PAPILLARY MUSCLES MITRAL VALVE This valve, also known as the bicuspid valve, opens the path for the blood from the left auricle toward the ventricle and then prevents it from returning. SEPTUM The interventricular wall that separates the two inferior cavities PULMONARY VALVE Through this valve blood to be oxygenated passes from the right ventricle toward the pulmonary artery. AORTA The principal artery of the body. Oxygenated blood exits through this artery. AORTIC VALVE regulates the passage of the oxygenated blood toward the aorta. VALVES The valves control the blood flow between the atria and the ventricles. In the graphic above (right) the pressure of the blood pumped by the heart forces the valve open. The graphic below shows that once the blood has entered, its own weight leads to a pressure reversal that causes the valve to close. IS THE AVERAGE WEIGHT OF AN ADULT HEART (RANGE: 7 TO 14 OUNCES [200 TO 400 G]). The Return Flow of Blood These cells are phantom cells, because all they contain is a large amount of hemoglobin, a protein that has a great affinity for combining with oxygen. The red blood cells, which circulate in the blood, bring oxygen to the cells that need it, and they also remove a small part of the carbon dioxide that the cells are discarding as waste. Because they cannot reproduce themselves, they must be replaced by new red blood cells that are produced by the bone marrow. AORTA PULMONARY VEIN PORTAL VEIN PULMONARY ARTERY Network of vessels in the upper part of the body Network of vessels in the lower part of the body Network of vessels in the liver Network of vessels in the right lung Network of vessels in the left lung Network of vessels in the digestive apparatus SUPERIOR VENA CAVA INFERIOR VENA CAVA IS THE APPROXIMATE NUMBER OF TIMES THAT THE HEART BEATS PER MINUTE. IT PUMPS 2,000 GALLONS (8,000 L) OF BLOOD PER DAY. 70 A RED BLOOD CELL TRAVERSES THE BODY IN 20 SECONDS. THEREFORE, THE DISTANCE THAT IT TRAVELS AMOUNTS TO 12,000 MILES (19,000 KM). 1 ATRIAL SYSTOLE The atria contract to push the blood down toward the ventricles. The right ventricle receives the blood that will have to be sent to the lungs to be oxygenated. The left ventricle receives blood coming from the lungs, which is already oxygenated and must be pumped toward the aorta. 2 VENTRICULAR SYSTOLE The ventricles contract after a brief pause. The systole, or contraction, of the right ventricle sends impure blood to the lungs. The contraction of the left ventricle pumps the already oxygenated blood toward the aorta; it is ready for distribution throughout the body. 3 RIGHT VENTRICLE receives the blood from its atrium and pumps it to the pulmonary valve. TENDINOUS CORDS These are the small fibrous threads whosefunction is to fasten the ends of the tricuspid valve to the heart wall. LEFT RIGHT VALVE TENDINOUS CORDS All About the Heart 10ounces (300 g) 20seconds
  24. 24. 40 INTERNAL SYSTEMS AND ORGANS Components of the Blood T he blood is a liquid tissue composed of water, dissolved substances, and blood cells. The blood circulates inside the blood vessels thanks to the impulse it receives from the contraction of the heart. A principal function of the blood is to distribute nutrients to all the cells of the body. For example, the red blood cells (erythrocytes) carry oxygen, which associates with the hemoglobin, a substance in the cell responsible for the blood's red color. The blood also contains white blood cells and platelets that protect the body in various ways. THE APPROXIMATE VOLUME OF BLOOD PRESENT IN A HUMAN ADULT 5quarts (4.7 l) Blood Components The blood is a tissue, and as such it is characterized by the same type of cells and intercellular substance as tissue. It is distinguished from the rest of the tissues in the human body by an abundance of intercellular material, which consists primarily of water. The intercellular material, called plasma, is yellow, and it contains abundant nutrients and other substances, such as hormones and antibodies, that take part in various physiological processes. White Blood Cells, or Leukocytes This is what a leukocyte, or white blood cell, looks like swimming in blood plasma. They are called white because that is their color when viewed under a microscope. Platelets are cell fragments that have separated from the megakaryocytes, cells located in the bone marrow. They have a role in blood coagulation. Next to the red blood cells, the platelets are the most abundant component of the blood. Red Blood Cells These cells are phantom cells, because all they contain is a large amount of hemoglobin, a protein that has a great affinity for combining with oxygen. The red blood cells, which circulate in the blood, bring oxygen to the cells that need it, and they also remove a small part of the carbon dioxide that the cells are discarding as waste. Because they cannot reproduce themselves, they must be replaced by new red blood cells that are produced by the bone marrow. Plasma Red and white blood cells and platelets (which contribute to coagulation) make up 45 percent of the blood. The remaining 55 percent is plasma, a fluid that is 90 percent water and the rest various nutrients. Red Blood Cells 4 to 6 million White Blood Cells 4,500 to 11,000 Platelets 150,000 to 400,000 Normal pH 7.40 COMPONENTS OF THE BLOOD PER 0.00006 cubic inch (1 cu ml) DAILY PRODUCTION IN MILLIONS 200,000 10,000 400,000 Red Blood Cells White Blood Cells Platelets COMPOSITION GRANULOCYTES Neutrophils Eosinophils Basophils AGRANULOCYTES Lymphocytes Monocytes 0.0003 INCH (0.008 MM) 90% Water 8% Protein 2% other (salts, nutrients, glucose, amino acid fats, and waste) 0.0003 INCH (0.008 MM) 0.0003 INCH (0.008 MM) HUMAN BODY I 41 Each person belongs to a blood group. Within the ABO system the groups are A, B, AB, and O. Each group is also identified with an antigen, or Rh factor, that is present in the red blood cells of 85 percent of the population. It is of vital importance to know what blood group a person belongs to so as to give only the right type during a blood transfusion. The immune system, via antibodies and antigens, will accept the body's own blood type but will reject the wrong type. GROUP A An individual with red blood cells with antigen A in its membranes belongs to blood group A, and that person's plasma has antibodies against type B. These antibodies recognize red blood cells with antigen B in their membranes as foreign. FLEXIBILITY Red blood cells are flexible and take on a bell shape in order to pass through the thinnest blood vessels. COMPATIBILITY Donors of group O can give blood to any group, but group AB donors can give only to others with AB blood. The possibility of blood donation depends on the antibodies of the recipient. A B AB0 A B AB0 ANTI-B ANTIBODY ANTIGEN A ANTIGEN B ANTI-A ANTIBODY BICONCAVE FORM BELL-SHAPED GROUP B Members of this group have antigen B in the membrane of their red blood cells and anti-A antibodies in their blood plasma. GROUP AB Members of this group have antigen A and B in the membrane of their red blood cells and no antibodies in their blood plasma. GROUP O Members of this group have no antigens in the membranes of their erythrocytes and anti-A and anti-B antibodies in their blood plasma 1 2 3 4 The Blood Groups ANTIGEN A ANTIGEN B ANTI-B ANTIBODY ANTI-A ANTIBODY THE BLOOD MAINTAINS THE BODY AT THIS AVERAGE TEMPERATURE. 98.6ºF (37º C) IS THE PORTION OF BODY WEIGHT REPRESENTED BY THE BLOOD. 7%
  25. 25. Lymphatic System 42 INTERNAL SYSTEMS AND ORGANS HUMAN BODY I 43 I t accomplishes two basic functions: defense against foreign organisms (such as bacteria) and aid with transport of liquid and matter via the circulation of the lymph from the interstices of the tissue and from the digestive apparatus to the blood. About 3 to 4 quarts (2.8-3.7 l) of the liquid circulating in the system do not return. This liquid is known as lymph, and it is reabsorbed into the plasma only through the lymphatic vessels. The lymph contains cells called lymphocytes and macrophages, which are part of the immune system. One part of the liquid that exits from blood flow and distributes itself in the body returns only through the action of the lymphatic tissue, which reabsorbs it via the lymphatic capillaries and returns it to the blood via the lymphatic vessels. SPLEEN The largest lymphatic organ, it performs specific tasks, such as filtering the blood, producing white blood cells, and eliminating old blood cells. It also stores blood. The spleen can weigh between 3 and 9 ounces (100 and 250 g). It is about 5 inches (12 cm) long and 3 inches (7 cm) wide. THYMUS A gland consisting of two lobes, located in the upper section of the sternum. It develops during puberty and then begins to decline, transforming itself into a mass of connective tissue. The thymus transforms blood cells produced in the bone marrow into specialized T lymphocytes. PEYER'S PATCH Lymphatic tissue located in the lower region of the small intestine BONE MARROW The bone marrow generates white blood cells, or lymphocytes, within the bones. LEFT SUBCLAVIAN VEIN Has the same function as the right subclavian vein. The name derives from its location beneath the clavicle. TONSILS Similar to the ganglia, their tissue detects invading organisms. SPLEEN The main lymph organ for the entire body LYMPHATIC VESSELS receive the lymph from the lymphatic capillaries. POPLITEAL LYMPH NODES are located behind the knees, and they filter the lymph from the lower extremities. THYMUS transforms the white blood cells in the bone marrow into T lymphocytes. THORACIC DUCT sends the lymph to the left subclavian vein. INGUINAL LYMPH NODES filter the lymph from the lower regions of the body. 1 The lymphatic system generates lymphocytes (also found in the blood and in other tissue) and macrophages. Together they constitute the immune system. Here invading bacteria are devoured by a macrophage, and the B lymphocytes take information from the surface of the bacteria that they need to “recognize” other similar bacteria. 2 The B lymphocytes are activated and upon recognizing a pathogen divide themselves into plasmatic cells and memory cells. The plasmatic cells secrete thousands of antibody molecules per second, which are carried by the blood to the site of the infection. The memory cells retain the antigen information, and, when faced with a new invasion, will once again divide rapidly in order to deal with it. 3 The antibodies, also called “immunoglobin,” are protein molecules in the form of a “Y,” with arms unique to each specific type of antibody. It is this feature that attaches them to a specific antigen. Their function is to “mark” invaders, which can then be destroyed by the macrophages. Immune Response Lymphatic Tissue RIGHT SUBCLAVIAN VEIN brings the lymph from the upper part of the body to the lymphatic duct. AXILLARY LYMPHATIC GANGLIA The lymph from the chest and the arms is filtered just above the armpits. Lymphatic Network This network contains vessels that extend throughout the body and that filter the liquid that comes from the area surrounding the cells. The lymph circulates in only one direction and returns to the blood through the walls of small blood vessels. There are valves that prevent the lymph from flowing in the opposite direction. The lymph nodes filter harmful microorganisms from the lymph, which returns via blood vessels to maintain the equilibrium of the body's fluids. Together with the white blood cells, the lymph nodes are in charge of maintaining the immune system. ARTERIOLE BLOOD CAPILLARY LYMPHATIC CELL LYMPHATIC CAPILLARY VENULE DIRECTION OF BLOOD FLOW LYMPHATIC CELL INTERSTITIAL LIQUID penetrates through the ultra-fine spaces in the tissues. CAPILLARY CELLS lie along, but do not impede, the passage of fluid. VALVE opens when the liquid has passed. LATERAL AORTIC NODES Together with the thymus and the spleen, bone marrow constitutes the lymphatic system tissues, whose function is to mature the lymphocytes. BONE MARROW THE AMOUNT OF LIQUID THAT LEAVES THE BLOOD AND PASSES THROUGH THE SYSTEM DAILY, MOVING THROUGH THE TISSUES AND RETURNING TO THE BLOODSTREAM 6gallons (24 l)
  26. 26. 44 INTERNAL SYSTEMS AND ORGANS HUMAN BODY I 45 Lymph Node A lso called a lymph gland, this node has a round shape and is about 0.4 inch (1 cm) in diameter. Lymph nodes are distributed throughout the body—in the neck, armpits, groin, and popliteal bone (behind the knees), as well as in the thorax and abdomen. The lymphatic vessels are the ducts for the lymph and the pathways for communication among the lymph nodes. The battle of the immune system against invading germs takes place within the nodes, which then enlarge because of inflammation. THE AREA OF THE SKIN COVERED BY SWEAT GLANDS, A PART OF THE NATURAL DEFENSES THAT COMPLEMENT THE WORK OF THE GANGLIA IN THE IMMUNE SYSTEM 100(600 sq cm) THE COLOR OF INFLAMED SKIN WHEN BACTERIAL ACTION IN A WOUND CAUSES VASODILATION. THIS OCCURS BECAUSE THE BLOOD VESSELS EXPAND TO INCREASE BLOOD FLOW AS A MEANS OF DEFENSE. Red Invaders Disequilibrium can be caused in the homeostatic mechanisms of the human body, causing disease that may or may not be infectious. Noninfectious disease is usually produced by heredity, external factors, or lifestyle. Infections are brought on by parasitic organisms, such as bacteria, viruses, fungi, and protozoa (single-celled organisms belonging to the protist kingdom). Natural Defenses Besides the immune system, composed in part by the lymphatic system, the body has another group of resources called natural defenses, which people possess from birth. The body's first defensive barrier is the skin. If pathogenic agents succeed in passing through its filters, however, both the blood and the lymph possess specialized antimicrobial cells and chemical substances. A Defensive Filter The glands are covered with a sheath of connective tissue, which in turn forms an interior network that consists of clusters filled with lymphocytes. Their immunological functions are to filter the fluid that arrives via both the sanguine and lymphatic afferent veins, which then goes toward the heart to be returned to circulation via the efferent vessels and to produce immune cells for attacking and removing bacteria and carcinogenic cells. RESISTANT CAPSULE Has the function of enveloping and protecting the ganglia B LYMPHOCYTES acquire their immunological capacity in the bone marrow and in the liver of the fetus. RETICULAR FIBERS The networks that support the lymph nodes VEIN ARTERY T CELLS Specialized lymphocytes created in the thymus to help detect antigens EFFERENT LYMPHATIC VESSEL The conduit for the lymph that exits the ganglia and returns to the bloodstream VALVE regulates the passage of the lymph and prevents its reflux. LYMPHOCYTES White blood cells that, together with the macrophages, are the basis of the cellular component of the immune system. GERMINAL CENTER The area that contains B lymphocytes. There are two types: B cells, which produce antibodies, and T cells. MACROPHAGES Together with the lymphocytes, they are the basis of the immune system. They devour the invading bodies that are detected. AFFERENT LYMPHATIC VESSEL The afferent vessels carry the lymphatic liquid from the blood to the ganglia, or lymphatic nodes. A BACTERIA are found by the billions in any medium. Not all of them are harmful. Bacteria known as germs are pathogenic and release poisonous substances called toxins. B VIRUSES are not really living beings but chemical packages. They consist of genetic material. When they enter the body, they invade a cell, where they reproduce and then spread. C PROTOZOA are organisms that typically live in water and in soil. There are about 30 pathogenic species, which can produce a range of diseases from sleeping sickness and severe diarrhea to malaria. SWEAT GLAND secretes sweat, which helps to control body temperature, to eliminate toxins, and to protect the skin immunologically. MUCOUS SECRETIONS These secretions, called mucus, form in the upper and lower respiratory tracts, where they capture bacteria and carry them to the throat to be spit out. SALIVARY GLAND produces saliva, which contains bactericidal lysozymes. INTESTINAL MUCOSA The goblet cells in this membrane produce a defensive mucus. VAGINAL BACTERIA Under normal conditions, these are inoffensive, and they occupy areas that could be invaded by pathogenic bacteria. SEBACEOUS GLAND Located on the surface of the skin, this gland secretes a fatty substance called sebo. LACHRYMAL GLAND Secretes tears that protect the eyes. Tears, like saliva and perspiration, kill bacteria. square inches
  27. 27. 46 INTERNAL SYSTEMS AND ORGANS HUMAN BODY I 47 Respiratory System T he respiratory system organizes and activates respiration, a process by which the human body takes in air from the atmosphere, extracts the oxygen that the circulation will bring to all the cells, and returns to the air products it does not need, such as carbon dioxide. The basic steps are inhalation, through which air enters the nose and mouth, and exhalation, through which air is expelled. Both actions are usually involuntary and automatic. Respiration involves the airway that begins in the nose and continues through the pharynx, larynx, trachea, bronchi, bronchioles, and alveoli; however, respiration occurs primarily in the two lungs, which are essentially bellows whose job it is to collect oxygen from the air. The oxygen is then distributed to the entire body via the blood. Component Percentage in Percentage of Inhaled Air Exhaled Air Nitrogen 78.6 78.6 Oxygen 20.8 15.6 Carbon Dioxide 0.04 4 Water Vapor 0.56 1.8 Total 100 100 The air enters the nasal cavity, where it is heated, cleaned, and humidified (it also enters through the mouth). The air passes through the pharynx, where the tonsils intercept and destroy harmful organisms. The air passes through the larynx, whose upper part, the epiglottis, a cartilaginous section, prevents food from passing into the larynx when swallowing. From the larynx the air goes into the esophagus. The air passes through the trachea, a tube lined with cilia and consisting of rings of cartilage that prevent its deformation. The trachea transports air to and from the lungs. In the thoracic region the trachea branches into two bronchi, which are subdivided into smaller branches, the bronchioles, which in turn carry the air to the pulmonary alveoli, elastic structures shaped like sacs where gas exchange occurs. From the alveoli the oxygen passes into the blood and then from the blood to the tissues of the body. The carbon dioxide exits the bloodstream and travels toward the alveoli to be subsequently exhaled. Exhaled air contains more carbon dioxide and less oxygen than inhaled air. 1 2 3 4 5 6 HAIRS The interior of the trachea is covered with hairs (cilia), which, like the hairs in the nose, capture dust or impurities carried by the air. TRACHEA The great respiratory pathway between the larynx and the bronchi LARYNX A pharynx and trachea. It participates in phonation. PHARYNX The muscular tract in the neck. Food and air pass through it. LUNGS Two organs that take oxygen from the air EPIGLOTTIS THYROID CARTILAGE (ADAM'S APPLE) VOCAL CORDS The larynx also participates in phonation, or the emission of the voice. It does this with the two lower of the four small elastic muscles, called vocal cords. RING Cartilaginous ring of the trachea BRONCHI Two fibrous cartilaginous tubes, which begin in the trachea and terminate in the lungs DIAPHRAGM Membrane primarily consisting of muscular fiber that separates the thoracic cavity from the abdominal cavity Legend OXYGENATED BLOOD DEOXYGENATED BLOOD THE APPROXIMATE VOLUME OF AIR THAT ENTERS AND EXITS THE LUNGS DURING ONE MINUTE OF BREATHING 6quarts (5.5 l) WE NORMALLY BREATHE BETWEEN 15 AND 16 TIMES A MINUTE. 15 WHAT ENTERS AND WHAT EXITS Route Larynx The resonance box that houses the vocal cords; it consists of various components of cartilaginous tissue. One of these components can be identified externally: it is the Adam's apple, or thyroid cartilage, located in the middle of the throat. The larynx is important for respiration because it links the pharynx with the trachea and ensures the free passage of air entering and leaving the lungs. It closes the epiglottis like a door when the organism is ingesting food in order to prevent food from entering the airway. 1 2 3 4 5 6 TRACHEA The great pathway for incoming air, which divides into the two smaller bronchial tubes going to the lungs RESPIRATORY PROCESS
  28. 28. HUMAN BODY I 4948 INTERNAL SYSTEMS AND ORGANS Lungs T heir principal function is to exchange gases between the blood and the atmosphere. Inside the lungs, oxygen is taken from the air, and carbon dioxide is returned to the air. There are two lungs. The left lung has two lobes and one lingula, and it weighs approximately 30 ounces (800 g); the right lung has three lobes and weighs 35 ounces (1,000 g). Both lungs process the same amount of air. In men each lung has a capacity of 3 quarts (3.2 l), and in women, 2 quarts (2.1 l). The lungs fill most of the space in the thoracic cage surrounding the heart. Their major motions are inhalation (taking in air) and exhalation (expulsion). The pleural membranes, intercostal muscles, and diaphragm make this mobility possible. Inhalation The air enters. The diaphragm contracts and flattens. The external intercostal muscles contract, lifting the ribs upward. A space is created within the thorax into which the lungs expand. The air pressure in the lungs is less than that outside the body, and therefore air is inhaled. Exhalation The diaphragm relaxes and becomes dome- shaped. The external intercostal muscles relax. The ribs move downward and inward. The space within the thorax decreases, and the lungs are compressed. The air pressure within the lungs is greater than that outside of the body, and therefore the air is exhaled. Alveoli Hollow structures that terminate in the bronchioles. They store air, have the form of a globe or cluster of bubbles, and are active in gas exchange. The oxygen comes to the blood via the alveolar walls and then passes toward the capillary network. Carbon dioxide is transferred from the blood to the alveoli and is then exhaled. If the alveoli are damaged as the result of a pulmonary disorder, then there is less surface area available for the interchange of gases, and the person might feel shortness of breath. A Marvelous Pump The respiratory system accomplishes its functions by combining a series of involuntary and automatic movements. The lungs, opening and closing like bellows, make inhalation possible by increasing their capacity to take in air, which is then exhaled when the bellows close. Inside the lungs the first stage of processing the gases that came in through the nose and the trachea is accomplished. Once the exchange of oxygen to be absorbed and carbon dioxide to be expelled occurs, the next stages can be accomplished: transport of the gases and delivery of oxygen to the cells and tissues. 30,000THE NUMBER OF BRONCHIOLES, OR TINY BRANCHINGS OF THE BRONCHI, IN EACH LUNG 350millionTHE NUMBER OF ALVEOLI IN EACH LUNG (700 MILLION FOR BOTH TOGETHER) BRONCHIAL TREE The complex of tubes that bring air to and from the lungs. They diminish in size from the trachea and subdivide into bronchioles and alveoli. BRONCHIOLES are thinner than a human hair. They secrete mucus. BRONCHI One for each lung; the two great pathways into which the trachea is divided TRACHEA The trachea is reinforced with C-shaped pieces of cartilage. PULMONARY ARTERY The only blue artery. The oxygen- poor blood goes from the right side of the heart to the lungs to pick up oxygen. AORTAL ARTERY Recharged with oxygen from the lungs, the blood returns to the heart and then circulates through the entire body. ALVEOLI If dust or microorganisms enter, the macrophage cells defend against them.defienden. PLEURAL MEMBRANES are primarily muscular and allow the lungs to move within the rib cage. 3 2 1 The alveolar cavity fills with air. The red arrows indicate the direction the oxygen travels toward the red blood cells and then on toward the heart and the rest of the body. The blue indicates the direction the carbon dioxide travels to the red blood cells and the plasma from the heart so that the alveolar can return it to the lungs. The complete operation of exchange is hematosis. The carbon dioxide will be returned to the lungs by the venae cavae and exhaled. HOW IT WORKS Airflow Intercostal Muscles Ribs Lungs Diaphragm Airflow Intercostal Muscles Alveolar Wall Entry and Exit of Air Red Blood Cells Liquid Surfactant Alveolar Cavity Capillary Intercostal Muscles Ribs Lungs Diaphragm
  29. 29. 50 INTERNAL SYSTEMS AND ORGANS HUMAN BODY I 51 Digestive System T he digestive system is the protagonist of a phenomenal operation that transforms food into fuel for the entire body. The process begins with ingestion through the mouth and esophagus and continues with digestion in the stomach, the small intestine, and the large intestine, from which the feces are evacuated by the rectum and anus. By then the task will have involved important chemical components, such as bile, produced by the liver, and other enzymes, produced by the pancreas, by which the food is converted into nutrients. Separating the useful from the useless requires the filtering of the kidneys, which discard the waste in urine. 00:00:10 00:00:00 03:00:00 08:00:00 Between 20 and 44 hours after having entered the mouth as food, the residue that was converted into semisolid feces in the previous stage arrives at the rectum. The waste will be evacuated through the anus as excrement. 24:00 The First Step: Ingestion The digestive process begins with the mouth, the entry point to the large tract that changes in form and function and ends at the rectum and anus. The tongue and teeth are the first specialists in the task. The tongue is in charge of tasting and positioning the food, which is cut and ground by the teeth. This synchronized activity includes the maxillary bones, which are controlled by their corresponding muscles. The palate, in the upper part of the mouth, prevents food from passing into the nose. The natural route of the food is down the esophagus to the stomach. Teeth There are 32 teeth, and they are extremely hard, a condition necessary for chewing food. There are eight incisors, four canines, eight premolars, and 12 molars. Humans develop two sets of teeth, a provisional or temporary set (the baby teeth) and a permanent set (adult teeth). The first temporary teeth appear between six and 12 months of age. At 20 years of age the process of replacement that began at about age five or six is complete. Digestion Chronology The process that converts food into nutrients begins a few seconds after the food is raised to the mouth and chewing begins. The average digestion time is about 32 hours, though digestion can range from 20 to 44 hours. Enzymes and Hormones The complex chemical processes that transform food are essentially accomplished by enzymes and hormones. Both types of substances are secreted by various glands of the digestive system, such as the salivary glands. Enzymes are substances that act as catalysts. Hormones are substances that regulate processes such as growth metabolism, reproduction, and organ function. ESOPHAGUS Its muscles force the bolus toward the stomach. The esophagus and stomach are separated by a sphincter. PHARYNX The muscles in the walls of the pharynx contract, forcing the bolus of chewed food into the esophagus. ROOT Entirely buried in the maxillary bone PULP Soft tissue that is the core of the tooth THE INSIDE OF A TOOTHTHE MOUTH A SET OF TEETH ENAMEL has no feeling and is the hardest substance in the body. DENTIN Sensitive to cold and heat, it is stronger than bone tissue. NERVES pass information about the tooth to the nervous system. CEMENT The thin layer that covers the roots and anchors them in the jawbone CANINES PREMOLARS MOLARS INCISORS 06:00:00 32A PERSON NORMALLY HAS THIS NUMBER OF TEETH. TractThe muscular movement called peristalsis pushes the food along. That is why it is possible to eat upside down or during weightlessness, as astronauts do. TONGUE Its notable flexibility makes eating possible. It also tastes the food. THE HARD PALATE The “roof” of the oral cavity. It is made of bone. THE SOFT PALATE Also called the velar palate, the palate keeps the food from going into the nose. 1 3 4 5 6 2 2 1 3 4 5 6 About 10 seconds after chewing has begun, the food is transformed into a moist alimentary bolus that makes its way through the pharynx to the esophagus and then to the stomach, where other changes will take place. Three hours after its arrival, the food leaves the stomach, which has accomplished its function. The first phase of digestion is over. The bolus now has a liquid and creamy consistency. Three hours later, the food that has been digested in the stomach arrives at the midpoint of the small intestine. At this point it is ready to be absorbed. Two hours later, the non-digested, watery residue arrives at the junction of the small and large intestines. The useless material rejected by the body's chemical selectors continues its course, and it is now prepared to be expelled from the organism in the form of feces. The process begins when the food reaches the mouth. The entire organism is involved in the decision, but it is the digestive system that plays the main role. The first steps are taken by the teeth and the tongue, aided by the salivary glands, which provide saliva to moisten the alimentary bolus. The morsels are chewed so that they can pass through the esophagus. 20:00:00The alimentary residue remains in the large intestine between 12 and 28 hours. In this part of the process the residue is converted into semisolid feces. 10inches (25 cm) IS THE LENGTH OF THE ESOPHAGUS.